This application is related to the field of digital communications and more specifically to dynamically adapting the transmission characteristics of a transmitting modem. FIG. 1 illustrates a block diagram of a conventional digital communication system 100. In this system transmitting modem 110 (modulator/demodulator) receives or accepts digital signal 120 and using well-known methods converts digital signal 120 into analog format. Analog signal 125 is then transmitted over network 135. For example, analog signal 125 may be transmitted, as shown, in a PCM (Pulse Coded Modulation) format.
Analog signal 125 propagates through network 135 and then through connection 145 is applied to receiving modem 150. Modem 150, using well known methods, converts analog signal 140 to digital form 155. The bit-rate and interleaver setting for the transmission is typically fixed to transmit a maximum amount of data bits over the network without errors.
However, noise, multi-path, fading and similar factors contribute to inducing errors in the reception of the transmitted analog signal. To compensate for such errors in transmission, the receiving system can request the transmitting site to re-transmit portions of, or even the entire original message. Repeating a transmission, however, reduces the efficiency of the network transmission, as no new information is transmitted in each re-transmission. Typically, a modem provides numerous bit rates that may be selected for the transmission of data bits. A maximum rate, for example, 9600 bits per second, may provide a high throughput, but requires a low noise interfering channel. Whereas, a minimum bit rate, for example 75 bits per second, may provide a sufficient throughput in a very noisy channel. Other rates less than the maximum provide lower throughputs, but with corresponding increases in robustness.
Another feature offered by a typical modem is the ability to use different interleaver settings to compensate for or combat the effects of a fading channel where errors are distributed unevenly. A typical modem may support six different interleaver settings with latencies as short as 0.12 seconds and as long as 8.61 seconds. An interleaver block provides enhanced error correction by spreading a random burst of errors over a larger number of data bits. This is advantageous as it allows for a more effective use of a forward error correction scheme to correct some or all of the errors detected in transmission. The longer the interleaver setting, the more capable it is to correcting larger bursts of errors, at the expense of increased latency in modulating a transmission and in the receiver turning around. Shorter interleavers provide reduced latency, but are not as robust in presence of multi-path.
Accordingly, a system is needed that dynamically adjusts the modem transmission characteristics in response to unknown and unpredictable changes in channel noise and multi-path to achieve a high data throughput.
Embodiments of a method and system for dynamically determining transmission characteristics of a modem transmitting information over a network is herein disclosed. In one embodiment, a method comprises the steps of determining a plurality of measured characteristics associated with a plurality of received samples collected over a known period, suggesting a first transmission characteristic from a plurality of known first transmission characteristics associated with a selected second measured characteristic based on a first measured characteristic in relation to a threshold value associated with each of the known first transmission characteristics, adjusting the suggested transmission characteristic dependent upon a third measured characteristic, and providing the suggested characteristics to the network. The method further comprises the steps of validating the suggested characteristics and transmitting a next packet using validated transmission characteristics.
It is to be understood that these drawings are solely for purposes of illustrating the concepts of the invention and are not intended as a definition of the limits of the invention. The embodiments shown in FIGS. 1 through 4 and described in the accompanying detailed description are to be used as illustrative embodiments and should not be construed as the only manner of practicing the invention. Also, the same reference numerals, possibly supplemented with reference characters where appropriate, have been used to identify similar elements.